The recent rapid growth in wireless communication adds the mobility to information services. However, for the vehicles traveling at high speed, such as cars and rapid railway, the service similar to wireless local area network (WLAN) is still not available. The transportation safety mechanism is one of the major issues in the car market. As more and more electronic technologies, such as global positioning system (GPS) and reverse radar, become the standard options for most vehicles, the safer and inexpensive collision prevention mechanism is becoming the next wave for market competition.
The general communication environment is moving from the pedestrian towards the vehicles in three directions. The first is the telematics service, such as remote diagnostics, which requires the cart to be connected to the back-end server for transmitting and receiving information to access network resources. The second is the communication for connecting one car to another for exchanging the sensed data and information, and exchanging the information between a car and an infrastructure, such as electronic toll, and inter-vehicle warning communication. The third is to provide connection of portable devices with the vehicle so that the vehicle information can be easily transmitted to the portable devices.
The global vehicle telematics service can be provided with the help of the wide-coverage 3G wireless communication or GPS. The stationary or low speed connection of portable devices to the network can be accomplished by the hotspot or the fixed WLAN access.
U.S. Pat. No. 6,954,421 disclosed an orthogonal frequency division multiplexing (OFDM) receiver device. FIG. 1 shows a schematic view of a channel estimation method of the receiver device. As shown in FIG. 1, the receiver device uses four pilot signals for four-point channel estimation values. The linear interpolation is performed on the channel estimation values at these four points H(0,0)-H(0,3) to obtain the channel estimation values H′(1,0)-H′(47,0) of a full transmission path, and the equalizer parameter is updated in real time to improve the channel estimation performance.
In the multi-path time-variant channel, the linear interpolation on four-point channel estimation can cause the resolution to drop as the interpolation range is large, which further results in the large estimation error, and the time-variant compensation effect deteriorates. The stability of wireless network access for high speed vehicles is poor when applying this method.
The major obstacle of the current wireless communication technology to overcome is how to apply the WLAN concept to the inter-vehicle communication and the communication for access points between vehicle and roadside, so that the vehicle has the inexpensive data communication functionality and can form a moving short-distance LAN for promoting driving safety and providing warning messages. The technology barrier is the signal detection and decoding at high speed because the estimation and decoding difficulties increase due to the time-variant channel effect caused by high Doppler frequency. The solution will require the synchronization, channel equalization and estimation, decoding mechanism to form an efficient combination to reduce the cost.